In the eastern United States, weather conditions have been conspiring with human activities to generate hazy skies across a broad area. Haze, or particle pollution, has been lingering in the skies over the Mississippi River Valley, the Deep South, the Mid-Atlantic, and the Southeast off and on since June 20, 2005. The air over the region has frequently been stable and humid—atmospheric conditions that keep the tiny aerosol particles produced by our vehicles, power plants, and fires hovering thickly in the air.

In this Moderate Resolution Imaging Spectroradiometer (MODIS) image from June 23, 2005, the gray haze hangs over the lower Midwest (left), plunges southward over the Gulf of Mexico (bottom), and flows off the East Coast (right) in a broad swath that veils the scalloped North Carolina coastline. The image is not seamless because it is made from observations collected during two consecutive overpasses of NASA’s Terra satellite. Terra passes over the United States in an east-to-west path, so the right side of the image came first. MODIS collected the left-hand part of the image about 90 minutes later, which is why the clouds don’t line up perfectly.

NASA, the Environmental Protection Agency (EPA), and the National Oceanic and Atmospheric Administration (NOAA) teamed up back in 2003 to use MODIS aerosol observations, NOAA weather forecasts, and EPA ground-based air quality observations to make regional haze predictions. According to forecast discussions in the days leading up to June 23, haze-laden air from the Ohio Valley and Upper Midwest spread over the Appalachian Mountain region, and then moved into the Mid-Atlantic and the Gulf Coast states. On June 22, haze flowed out to the Atlantic, but easterly winds moved some of it back over the Southeast. By the time this image was captured on June 23, haze was once again spreading offshore.